It showed that most exposure (86 per cent) is from natural sources. Contrary to many people’s assumption, just 0.3 per cent of the total comes from artificial sources such as Sellafield, Chernobyl or weapons testing, according the institute’s report.

Once again the numbers highlight the risks associated with natural exposures from radon gas, which seeps from the ground in areas where there is a lot of granite rock.

It blows away on the wind, but can build up when trapped under buildings, leading to sharply rising exposures depending on conditions. It accounts for more than half, 55.2 per cent, of our total annual radiation exposures.

Its impact is not trivial given up to 250 cases of lung cancer arise each year because of radon, the report says. It is the second biggest cause of lung cancer after smoking.

“The assessment clearly identifies radon as the primary source of radiation exposure in Ireland,” said Dr Ann McGarry, chief executive of the institute.

Our radon dose is high compared to other European countries because radon is plentiful here, she said. This can lead to situations where “some families in Ireland are exposed to extremely high radiation doses in their homes”.

This makes it a health protection issue given the numbers of people who may have a problem with radon in their homes.

She adds, however, that there are low cost remedial changes that can reduce or eliminate radon exposures of this kind.

The second biggest exposure and the highest man-made exposure relates to medical uses, mostly x-rays and diagnostic tests that are based on radioactivity. This accounts for 13.5 per cent of total exposures.

Other natural exposures include thoron - a slightly different form of radon - cosmic rays from space, other natural radioactivity and also natural radioactivity in our food.

People concerned about radon levels in their homes can carry out a simple test available from the institute. It costs about €50 and more information is available from www.rpii.ie.